Eight people have been arrested in raids targeting a gang suspected of taking cash to help Iranian asylum seekers get into Britain.
UK Border Agency (UKBA) officers worked with the Spanish police and airlines including Ryanair to stage the crackdown on a criminal network working across Europe.
It is alleged the gang helps Iranians get to the UK from mainland Europe by giving them fake travel documents and organising travel.
A series of early-morning raids were carried out in London on Monday and six men and one woman aged between 23 and 56 were arrested. A further arrest was made yesterday in Hull. Computers, documents and mobile phones were also seized.
Another 11 people were arrested in raids in Madrid and Alicante.
Chris Foster from UKBA said: "This investigation is targeting an organised network suspected of being involved in a systematic attempt to evade the UK's immigration controls.
"People-smuggling is an international crime which requires international co-operation, so we have been working very closely with our Spanish law-enforcement colleagues from the outset. Our investigation will continue with the evidence we have seized."
Six of the arrests were in north London. Four men, aged 23, 29, 38 and 56, and a woman aged 23, were held in Mill Hill, while a 44-year-old man was detained in Edgware.
The seventh, a 46-year-old man, was arrested in Kensington, central London. They were all held on suspicion of conspiring to facilitate an asylum seeker for gain.
Officers made a further arrest in Spring Bank, Hull, where a 46-year-old man was detained on suspicion of facilitation offences.